Directional broad band antenna array



Jan.v 28, 1969 Filed `Feb. 28, 1964 ATTORNEY United States Patent O 3,424 984 DIRECTIONAL BROAD BAND ANTENNA ARRAY John Harold Dunlavy, Jr., Silver Spring, Md., assignor to Antenna Research Associates, Inc., Beltsville, Md., a corporation of Texas Filed Feb. 28, 1964, Ser. No. 348,069 U.S. Cl. 325-384 Int. Cl. H04b 1/18 ABSTRACT F THE DISCLOSURE This specification discloses a directional receiving antenna array comprising spaced dipoles connected to feed a common output through separate channels. Each of the channels contain active elements to electrically isolate the dipoles from one another and one of the channels also contains a delay line.

This invention relates to antennas and has reference to a broad band dipole array of unusually small size.

Active elements in receiving antennas may be defined as power consuming electronic components which, by their physical or electrical location, contribute to the op erational characteristics of an antenna or an antenna array as opposed to a radio receiver, itself. U.S. Patent 2,578,- 973 to Hills and U.S. Patent No, 3,098,973 to Wickersham are examples of public disclosures which teach the use of active elements in antennas for various purposes.

The present invention involves the combination in one embodiment of certain characteristics of both passive and active elements to achieve a substantial diminution of the physical dimensions of a dipole array while impa-rting desirable broad band characteristics to the system and retaining directional characteristics over a very wide range of frequencies. More particula-rly, the present invention involves the use of certain active elements having high input impedances to realize an approximation of open circuit voltages presented by short dipole elements. At the same time, the invention provides electrical simulation of wide physical spacing between array elements actually close to one another and electrically isolates elements of an array one from another to obviate problems of mutual impedances. For a broad band antenna, physical size criteria can be approached in terms of aperture for most applications. A sound approach dictates that for most high frequency applications the antenna need only be large enough to receive sufiicient atmospheric noise (assuming the signal received is above atmospheric noise) to mask receiver input noise for optimum reception efiiciency. A systems signal-to noise ratio will not be impaired if receiver noise is small compared to atmospheric noise. In the high frequency range, reduction of physical dimensions and consequent structural requirements are of obvious value where desireable electrical characteristics are not impaired or are even improved.

Accordingly, an object of the present invention is to provide an antenna array which is small in size with respect to its frequency range as compared to other arrays known heretofore.

Another object of the invention is to provide a small dipole array having desirable characteristics over a wide range of frequencies.

A further object of the invention is to provide an antenna array which retains useful directional characteristics over a wide range of frequencies.

Another object of the invention is to provide an array having active elements which may be incorporated into a relatively small structure.

A particular object of the invention is to provide an an- 3,424,984 Patented Jan. 28, 1969 tenna array of small size and broad bandwidth characteristics which can maintain directivity throughout the high frequency range.

These and other objects will become apparent from the following description a-nd the accompanying drawing wherein:

The figure is a schematic diagram of a dipole array embodying active elements therein.

Generally, the invention may incorporate spaced dipoles of small size which feed a common terminal through active elements of separate amplification channels having characteristics which favorably utilize the impedances of the dipoles and the advantages of electrically isolating elements of an array.

With particular reference to the drawing, dipole elements 10 and 11 are respectively joined at their next adjacent terminations 12 and 13 to a pair of conductors 14 and 15 which, together, comprise a three hundred ohm twin lead transmission line. The other ends of the conductors 14 and 15 are respectively electrically connected to terminals 16 and 17 of amplifier input lines 18 and 19. Active element amplifiers, as contemplated in the present invention, can be made satisfactorily in a number of configurations, but it is desirable that each active element amplifier have a high impedance output and that each amplifier be made as close in electrical characteristics to all other associated active element amplifiers as is possible. Thus, input lines 18 and 19 respectively feed high impedance RC coupled first amplifier stages 20 and 21 which in turn respectively feed interstage conductors 22 and 23 which serve as inputs for respective second stage ampli. fiers 24 and 25 of the cathode follower type. The outputs 26 and 27 of the described two stage active element arnplifiers each feed a toroidal balun transformer having input impedance characteristics of two hundred ohms and an output impedance of fifty ohms; the balun 28 is provided with a ground connection 29. The secondary output 30 of the balun 28 is provided with a terminal 31 electrically connected to one end of a fifty ohm delay line 32. The other end of the delay line 32 is connected to a common terminal 33 for all outputs of the array.

Those elements described heretofore may be considered as constituting a first channel of the array; with the exception of the absence of a delay line, elements constituting a second channel of the array are in all respects identical to those described for the first channel. These channels may be considered to be feedlines, which are of different effective lengths because of the delay line 32 and which are connected to feed signals from the dipoles to the output terminal 33 introducing a fixed time delay displacement between the signals. Thus, the common terminal 33 is connected to the secondary output line 34 of a second toroidal balun 35 being in all respects identical to the toroidal balun 28 and having a ground connecktion 36 in common therewith. Primary inputs of the balun 35 are respectively fed by the output lines 37 and 38 of separate cathode follower amplifier stages 39 a-nd 40; interstage conductors 41 and 42 which feed the cathode follower amplifing stages 39 and 40 are fed by the respective outputs of separate high impedance RC coupled amplifier stages 43 and 44 which are, in turn, respectively fed by input lines 4S and 46 having terminals 47 and 48 connected to the ends of transmission channel conductors 49 and 50 which, together, constitute a three hundred ohm twin lead transmission line. Next adjacent terminations 51 and 52 of dipole elements 53 and 54 are respectively connected to the other ends of the two conductors 49 and 50 of the twin lead transmission line.

Also, connected to the `common terminal 33 is the input line 55 of a four-to-one impedance transformer 56 having corresponding ends of its primary and secondary coils provided with a ground connection 57 wired in common with the ground connections 29 and 36 of the toroidal baluns 28 and 35. The secondary output 58 of the irnpedance transformer 56 feeds a grounded grid input arnplifier stage 59 which is RC coupled by an interstage conductor 60 to the input of a cathode follower output amplifier stage 61. The output 62 of the cathode follower amplifier stage 61 is fed to a radio receiver not shown.

In operation outputs of dipole elements and 11, are respectively fed by their twin lead transmission line 14-15 to separate two-stage amplifiers -25 having high input impedance each tending to match the impedance of a center fed dipole element 10-11 very small in length compared to the typical quarter wave length elements tuned to the low end of the high 4frequency band. Outputs of the two stage amplifiers 20-25 are fed to the toroidal balun 28 having the output 30 of its secondary connected to the delay line 32 which simulates additional physical spacing between the dipoles 10-11 and 53-54. The other dipole 53-54 likewise has its elements fed through two-stage amplifiers 39-44 having high input impedances and matched outputs to a balun 35. The common terminal 33 receives outputs from both dipoles and carries the sum or difference of amplified signals received therefrom according to the orientation of the array. The amplifiers fed from the dipole elements tend to isolate the dipoles from one another electrically and to eliminate so called mutual impedances which would otherwise tend to give narrow band width characteristics to the array. The pattern exhibited by the antenna over a `wide frequency range is an approximation of a cardioid.

A critical feature of the invention as expressed in this embodiment is the necessity for matching amplifiers with regard to transconductance in the separate channels to assure equal gain in each. Elements -between the common terminal 33 and final output line 62 do not affect or control any of the directivity parameters or functions of the array but serve to improve output and impedance matching for a receiver.

The invention is not limited to the exemplary construction herein shown and described but may be made in various ways within the scope of the appended claims.

What is claimed is:

1. An antenna array comprising:

a first dipole including two dipole elements,

two first channel amplifiers each having high impedance inputs,

a first twin lead transmission line respectively connecting said dipole elements to said high impedance inputs of said two first channel amplifiers,

a first balun transformer having the outputs of said two first channel amplifiers connected to the inputs thereof,

a common output terminal,

a delay line electrically connected between said cornmon output terminal and of said first balun transformer,

a second dipole spaced from said first dipole and having two dipole elements,

two second channel amplifiers each having high impedance inputs,

a second twin lead transmission line respectively connecting said dipole elements of said second dipole to said high impedance inputs of said two second channel amplifiers,

a second balun transformer having the outputs of said two second channel amplifiers connected to the inputs thereof,

and means electrically connecting the output of said second balun to said common output terminal.

2. In a dipole array including at least two centerfed dipoles and a common output terminal,

a plurality of substantially identical high impedance input amplifiers,

means connecting each elements of each dipole to the input of one and only one of said high impedance amplifiers,

a plurality of balun transformers each having only the outputs of such amplifiers as are fed from one of said dipoles connected to inputs thereof,

at least one delay line connecting an output of one of said balun transformers to said common output terminal,

and means connecting the outputs of the remainder of said balun transformers to said common output terminal.

3. The invention as defined in claim 1 and wherein said balun transformers `each include a toroidal core common to all windings thereof.

4. The invention as defined in claim 2 and wherein each of said plurality of amplifiers includes a high impedance R-C coupled input stage and a cathode follower output stage.

5. A broad band directional antenna array comprisa pair of spaced antenna elements;

a transmission channel;

a means of electrically isolating said antenna elements from each other to minimize mutual impedance effects therebetween and including a matched pair of unidirectional coupling means each connected to a respective one of said antenna elements for receiving input signals intercepted by said antenna elements and delivering to said transmission channel a combined signal at the same frequency as said input signals and representative of a combination of said input signals; and

a delay line inserted between at least one of said antenna elements and said transmission channel to introduce a phase displacement between the signals intercepted by said antenna elements to simulate additional physical spacing between said antenna elements, all of the phase displacement introduced between the signals intercepted by said antenna elements being provided entirely by said delay line.

6. A broad band directional antenna array comprising:

a pair of spaced antenna elements;

a transmission channel;

a unidirectional coupling network having two independent inputs vwith high electrical isolation therebetween for receiving input signals intercepted by said antenna elements and an output for delivering to said transmission (line) channel a combined signal at the same frequency as said input signals and representing said input signals; and

a delay line inserted between one of said antenna elements and said transmission channel to introduce a relative phase displacement between the signals intercepted by said antenna elements, all of the phase displacement introduced between the signals intercepted by said antenna elements being provided by said delay line.

7. A broad band directional antenna array comprising:

a pair of antenna elements spaced apart;

a transmission channel for delivering radio frequency energy from said antenna elements;

unidirectional coupling means having two independent inputs with high isolation therebetween to present mutual impedance between said antenna elements for receiving input signals intercepted by said antenna elements and an output for delivering to said transmission channel a signal at the same frequency as said input signals representing the algebraic difference of the signals applied to said inputs; and

lfeed lines connecting said antenna elements to said transmission channel through said unidirectional coupling means including a delay line in at least one of said feedlines to introduce a phase displacement into the signals intercepted by said antenna elements to simulate additional physical spacing therebetween,

all of the phase displacement introduced between the signals intercepted by said antenna elements being provided entirely by said delay line.

8. A broad band directional antenna array comprising:

a pair of spaced apart antenna elements;

a transmission channel;

directional coupling means having two independent inputs with high isolation therebetween and outputs for delivering algebraically combined input signals `unchanged in frequency to said transmission channel;

a delay line having a predetermined phase shift characteristic in combination with the electrical connections between portions of said array,

first transmission means connecting one of said antenna elements to said transmission channel through one of said independent inputs; and

second transmission means connecting the other of said antenna elements to said transmission channel through the other of said inputs and said/time delay device, all of the phase displacement introduced between the signals intercepted by said antenna elements being provided entirely by said delay line.

9. A broad Iband directional antenna system comprising:

a pair of spaced apart dipoles short in relation to signal wavelengths in the band of operation of said antenna system; and

a 'broad band unidirectional coupling means having an output and mutually isolated inputs connected to receive input signals intercepted by respective ones of said dipoles operating to prevent the flow of frequency-variable mutual currents between said dipoles through said unidirectional coupling means, and delivering to said output a signal at the same frequency as said input signals and representing the algebraic sum or difference of the two input signals, said coupling means including a delay line connected between one of said inputs and said output for introducing a phase displacement between said signals, the phase displacement introduced between the signals intercepted by dipoles being provided entirely by said delay line.

References Cited UNITED STATES PATENTS 6/1944 Garnet 343-854 XR 3/1966 Vogt 343-854 XR 5/1967 Blachier et al. 343-854 XR KATHLEEN 'H. CLAFFY, Primary Examiner.

5 R. S. BELL, Assistant Examiner.

U.S. Cl. X.R. 

